The present embodiments relate to determination of physiological cardiac parameters as a function of heart rate.
In the field of angiography, a number of techniques are known for obtaining information about a patient's heart. Most images (e.g., X-ray images) of the heart are taken using the technique of digital subtraction angiography (DSA). DSA involves a contrast agent being administered to the patient such that, on images of the heart, the blood vessels filled with contrast agent and the heart filled with contrast agent may be distinguished clearly. If mask images that had been taken before the contrast agent was introduced into the region to be X-rayed in a patient who, compared to the situation with the contrast images, has not been moved, are subtracted from the images taken using contrast agent (e.g., “contrast images”), all that remains, apart from noise effects, are signal components of the contrast agent. An excellent evaluation of the resulting DSA images may thus be possible.
DSA is not only used in cases where a detailed mapping or a detailed evaluation of a patient's cardiovascular structure is to be provided, but also when dynamic information relating to the heart (e.g., a cardiac motion analysis) is to be acquired. Alongside two-dimensional digital subtraction angiography, the reconstruction of three-dimensional reconstructed data sets for various cardiac phases from two-dimensional projection images has also been suggested. A four-dimensional angiography data set showing the motion of the heart and the surrounding blood vessels throughout an entire cardiac cycle is thus generated, consequently showing a three-dimensional volume pumped throughout a cardiac cycle. The fourth dimension in such image data sets relates to the time factor.
In order to record such four-dimensional angiography image data sets, an X-ray device with, for example, a C-arm may be used in an angiography unit. This involves recording projection images in various projection directions at various points of time in the cardiac cycle. The projection images recorded are assigned to different cardiac phases (e.g., time periods in the cardiac cycle), which provides that the cardiac cycle is broken up into different time segments. Each set of projection images recorded within a time segment is sorted into a group of projection images. Each of these groups of projection images is used to generate a three-dimensional reconstruction image data set assigned in each case to the time segment. If these three-dimensional reconstruction image data sets are now put together according to the time order for the cardiac cycle, the four-dimensional angiography image data set is generated.
In order to counteract effects due to irregularity in cardiac motion and the such, US 2013/0336450 A1, issued as U.S. Pat. No. 9,036,780 B2 on May 19, 2015, proposes that projection images be recorded such that at least one recording parameter describing the time progression in the recording of the projection images is selected as a function of a cardiac stimulation carried out to provide a stable heart rate during the recording such that the recording of the projection images is synchronized with the cardiac cycle. Thus, by skillful selection of the recording time and/or of the movement of the C-arm, it therefore becomes possible to synchronize the time progression (e.g., the “timing”) of the recording of the projection images with the cardiac cycle such that the projection images for each time segment in the cardiac cycle are recorded. The projection images are thus distributed equally over the projection directions. A complete reconstruction for the individual cardiac phases may be achieved with as few artifacts as possible.
A known method of producing a stable heart rate is carrying out “pacing”. In connection with the recording of four-dimensional image data sets, “slow cardiac pacing”, where the heart rate tends to be in the lower range (e.g., lower than 140 beats per minute (bpm)) is provided, such that the significance of induced ventricular tachycardia is extremely slight. In this way, “ventricular flutter” is avoided.
Cardiac investigations including four-dimensional digital subtraction angiography, for example, aim to obtain prognostic cardiac diagnostic parameters that may predict the extent and severity of the disease, a risk of cardiac infarction and the like. Such known diagnostic parameters are, for example, the Duke score, the WMSI score (e.g., peak wall motion score index), the relationship between force (e.g., contraction) and heart rate, described by the Bowditch effect, the systolic volume index, the cardiac ejection fraction (EF), cardiac perfusion parameters and the like. In order to be able to calculate these diagnostic parameters, various physiological cardiac parameters (e.g., cardiac parameters relating to the heart wall that may be acquired from a segmentation of the heart muscle, parameters relating to the lumen and parameters relating to the heart's dynamics) may be provided.
Most of these cardiac parameters and diagnostic parameters are also dependent on the frequency of the heartbeat (e.g., heart rate). In order to make it possible to obtain the cardiac parameters and from these the diagnostic parameters also at other heart rates (e.g., at higher heart rates), it is known practice, for example, to administer drugs that stimulate the heart rate so that magnetic resonance images and/or ultrasound images of the heart and surroundings of the heart may be generated. For example, the method of pacing stress echocardiography is known in the field of ultrasound. However, this only allows numerical determinations of cardiac parameters for various heart rates to be carried out. In an angiography unit, however, C-arm X-ray devices are more common because C-arm X-ray devices provide the option of digital subtraction angiography.